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Lesson 1.1

Data Analysis 1 Picturing Data

Goal

Explore different types of graphs and draw a line of best fit.

Skills Focus

Interpret Graphs, Analyze Data

Build Connections

A graph can be thought of as a “picture” of data. Graphs are useful for scientists because they can reveal patterns or trends that words and tables cannot. Three types of graphs typically used to display scientific data are circle graphs, bar graphs, and line graphs.

Circle graphs, or pie charts, display data as part of a whole. Each “slice” represents a distinct category. Circle graphs can be used only when you have data for all categories you are comparing. You could use a circle to compare the amount of time you spent sleeping, being active, or being inactive during a 24-hour period.

Bar graphs are used to compare data from different categories. In a bar graph, the dependent variable represents a category that is not represented by a number. For example, you could use a bar graph to compare extinction rates for different types of animals. The animal groups are marked along the x-axis. The rate of extinction, the independent variable, is plotted along the y-axis.

Line graphs are used when you have numerical data for both the dependent and independent variables. A line graph shows how one variable changes in response to another variable. The independent, or manipulated, variable is plotted along the x-axis. The dependent, or responding, variable is plotted along the y-axis. By drawing a line from point to point on the graph, you may notice a trend that will allow you to make a prediction. Sometimes, if the data are scattered, you will need to draw a line of best fit to help you see a trend. A line of best fit is a straight line drawn through the data points so the same number of points are above the line as below the line.

In this four-part activity, you will convert data tables into graphs. In Parts A and B, you will need to decide which type of graph to make.

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Part A: Trees of the Rain Forest

A rain forest is divided into four layers. The bottom layer is the forest floor, which gets almost no light because of the trees. The next three layers are characterized by different types of trees and the height they reach above the forest floor. The understory is 0–10 meters above the forest floor. It has young trees, shrubs, and other plants. It also includes some species of trees that are short when full grown. The canopy is a dense layer that forms 10–40 meters above the forest floor.

Most species of the rain forest live in the canopy. The leaves of canopy trees spread out, forming a “roof” over the rain forest. The canopy lets in very little light and tends to spread raindrops from tropical downpours. The uppermost layer is the emergent layer, which is 40–70 meters above the forest floor. A few trees grow above the canopy. They either get full sun or drenching rain. Use the grid on page 221 to make an appropriate graph.

|Trees of the Rain Forest |

|Tree |Full Height (m) |

|Kapok |70 |

|Teak |46 |

|Ebony |30 |

|African yellowwood |20 |

|African oil palm |18 |

|Raffi a palm |12 |

|Cape fig |7 |

Analyze and Conclude

1. Evaluate What type of graph did you use and why? Identify the dependent and independent variables.

2. Interpret Data How many and what types of trees are found in each of the rain-forest layers? Suggest a way to highlight this information on your graph.

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Build Science Skills

Monkeys, flying squirrels, tree frogs, and anteaters are common to the rain forest. Each one occupies a different layer. Based on the information given, match each animal to a layer of the rain forest and explain your choice.

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Part B: Elements in the Human Body

The table shows the percent by mass of many elements found in the human body. Although the percentages are estimates, they are good indicators of relative amounts. Use the data to make an appropriate graph. Hint: It might make sense to group some data.

|Elements in Human Body |

|Element|Percent |Element |Percent |Element |Percent |Element |

| |by Mass | |by Mass | |by Mass | |

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Analyze and Conclude

1. Evaluate What type of graph did you use and why? Are there variables in this graph? Explain.

2. Interpret Data List the elements in the human body that are at least 1 percent of mass. Overall, what percent of body mass do these elements add up to?

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Build Science Skills

Most of the mass of the human body is water. The mass of water can vary from 60 to 90 percent. Do the data support this fact? Hint: Think of the chemical formula for water.

Part C: Hare and Lynx Pelts

One of the best-known examples of a population study came from the records of a fur-trading company in Canada. The Hudson’s Bay Company (HBC) kept records of its catches of hare and lynx over a long period of time. Charles Elton, an English ecologist, used the records to hypothesize about cycles in animal populations. The table shows the HBC data for hares and lynx pelts taken between 1845 and 1899.

|Comparison of HBC Hare and Lynx Pelts |

|Year |Hare |Lynx |

|Ham and cheese |15.5 |352 |

|Roast beef |18.8 |346 |

|Peanut butter and jelly |20.3 |439 |

|Turkey |5.0 |297 |

|Steak |14.1 |459 |

|Cheeseburger |22.7 |451 |

|Tuna salad |19.0 |383 |

|Egg salad |16.0 |380 |

Analyze and Conclude

1. Organize Data Before you plot the data points, you need to choose a dependent and independent variable. Explain your choice.

2. Graph Plot the data points. Then draw a line of best fit.

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3. Interpret Graphs What trend do you see when comparing fat content in the sandwiches to number of Calories?

Build Science Skills

The data in the table is not dependent on the serving size of the sandwich. Do you think data based on equal serving sizes would change the overall trend in the graph? Why or why not?

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